--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/lib/Serialization/GlobalModuleIndex.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,951 @@
+//===--- GlobalModuleIndex.cpp - Global Module Index ------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the GlobalModuleIndex class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Serialization/GlobalModuleIndex.h"
+#include "ASTReaderInternals.h"
+#include "clang/Basic/FileManager.h"
+#include "clang/Lex/HeaderSearch.h"
+#include "clang/Serialization/ASTBitCodes.h"
+#include "clang/Serialization/ModuleFile.h"
+#include "clang/Serialization/PCHContainerOperations.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Bitstream/BitstreamReader.h"
+#include "llvm/Bitstream/BitstreamWriter.h"
+#include "llvm/Support/DJB.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/FileUtilities.h"
+#include "llvm/Support/LockFileManager.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/OnDiskHashTable.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/TimeProfiler.h"
+#include <cstdio>
+using namespace clang;
+using namespace serialization;
+
+//----------------------------------------------------------------------------//
+// Shared constants
+//----------------------------------------------------------------------------//
+namespace {
+  enum {
+    /// The block containing the index.
+    GLOBAL_INDEX_BLOCK_ID = llvm::bitc::FIRST_APPLICATION_BLOCKID
+  };
+
+  /// Describes the record types in the index.
+  enum IndexRecordTypes {
+    /// Contains version information and potentially other metadata,
+    /// used to determine if we can read this global index file.
+    INDEX_METADATA,
+    /// Describes a module, including its file name and dependencies.
+    MODULE,
+    /// The index for identifiers.
+    IDENTIFIER_INDEX
+  };
+}
+
+/// The name of the global index file.
+static const char * const IndexFileName = "modules.idx";
+
+/// The global index file version.
+static const unsigned CurrentVersion = 1;
+
+//----------------------------------------------------------------------------//
+// Global module index reader.
+//----------------------------------------------------------------------------//
+
+namespace {
+
+/// Trait used to read the identifier index from the on-disk hash
+/// table.
+class IdentifierIndexReaderTrait {
+public:
+  typedef StringRef external_key_type;
+  typedef StringRef internal_key_type;
+  typedef SmallVector<unsigned, 2> data_type;
+  typedef unsigned hash_value_type;
+  typedef unsigned offset_type;
+
+  static bool EqualKey(const internal_key_type& a, const internal_key_type& b) {
+    return a == b;
+  }
+
+  static hash_value_type ComputeHash(const internal_key_type& a) {
+    return llvm::djbHash(a);
+  }
+
+  static std::pair<unsigned, unsigned>
+  ReadKeyDataLength(const unsigned char*& d) {
+    using namespace llvm::support;
+    unsigned KeyLen = endian::readNext<uint16_t, little, unaligned>(d);
+    unsigned DataLen = endian::readNext<uint16_t, little, unaligned>(d);
+    return std::make_pair(KeyLen, DataLen);
+  }
+
+  static const internal_key_type&
+  GetInternalKey(const external_key_type& x) { return x; }
+
+  static const external_key_type&
+  GetExternalKey(const internal_key_type& x) { return x; }
+
+  static internal_key_type ReadKey(const unsigned char* d, unsigned n) {
+    return StringRef((const char *)d, n);
+  }
+
+  static data_type ReadData(const internal_key_type& k,
+                            const unsigned char* d,
+                            unsigned DataLen) {
+    using namespace llvm::support;
+
+    data_type Result;
+    while (DataLen > 0) {
+      unsigned ID = endian::readNext<uint32_t, little, unaligned>(d);
+      Result.push_back(ID);
+      DataLen -= 4;
+    }
+
+    return Result;
+  }
+};
+
+typedef llvm::OnDiskIterableChainedHashTable<IdentifierIndexReaderTrait>
+    IdentifierIndexTable;
+
+}
+
+GlobalModuleIndex::GlobalModuleIndex(
+    std::unique_ptr<llvm::MemoryBuffer> IndexBuffer,
+    llvm::BitstreamCursor Cursor)
+    : Buffer(std::move(IndexBuffer)), IdentifierIndex(), NumIdentifierLookups(),
+      NumIdentifierLookupHits() {
+  auto Fail = [&](llvm::Error &&Err) {
+    report_fatal_error("Module index '" + Buffer->getBufferIdentifier() +
+                       "' failed: " + toString(std::move(Err)));
+  };
+
+  llvm::TimeTraceScope TimeScope("Module LoadIndex");
+  // Read the global index.
+  bool InGlobalIndexBlock = false;
+  bool Done = false;
+  while (!Done) {
+    llvm::BitstreamEntry Entry;
+    if (Expected<llvm::BitstreamEntry> Res = Cursor.advance())
+      Entry = Res.get();
+    else
+      Fail(Res.takeError());
+
+    switch (Entry.Kind) {
+    case llvm::BitstreamEntry::Error:
+      return;
+
+    case llvm::BitstreamEntry::EndBlock:
+      if (InGlobalIndexBlock) {
+        InGlobalIndexBlock = false;
+        Done = true;
+        continue;
+      }
+      return;
+
+
+    case llvm::BitstreamEntry::Record:
+      // Entries in the global index block are handled below.
+      if (InGlobalIndexBlock)
+        break;
+
+      return;
+
+    case llvm::BitstreamEntry::SubBlock:
+      if (!InGlobalIndexBlock && Entry.ID == GLOBAL_INDEX_BLOCK_ID) {
+        if (llvm::Error Err = Cursor.EnterSubBlock(GLOBAL_INDEX_BLOCK_ID))
+          Fail(std::move(Err));
+        InGlobalIndexBlock = true;
+      } else if (llvm::Error Err = Cursor.SkipBlock())
+        Fail(std::move(Err));
+      continue;
+    }
+
+    SmallVector<uint64_t, 64> Record;
+    StringRef Blob;
+    Expected<unsigned> MaybeIndexRecord =
+        Cursor.readRecord(Entry.ID, Record, &Blob);
+    if (!MaybeIndexRecord)
+      Fail(MaybeIndexRecord.takeError());
+    IndexRecordTypes IndexRecord =
+        static_cast<IndexRecordTypes>(MaybeIndexRecord.get());
+    switch (IndexRecord) {
+    case INDEX_METADATA:
+      // Make sure that the version matches.
+      if (Record.size() < 1 || Record[0] != CurrentVersion)
+        return;
+      break;
+
+    case MODULE: {
+      unsigned Idx = 0;
+      unsigned ID = Record[Idx++];
+
+      // Make room for this module's information.
+      if (ID == Modules.size())
+        Modules.push_back(ModuleInfo());
+      else
+        Modules.resize(ID + 1);
+
+      // Size/modification time for this module file at the time the
+      // global index was built.
+      Modules[ID].Size = Record[Idx++];
+      Modules[ID].ModTime = Record[Idx++];
+
+      // File name.
+      unsigned NameLen = Record[Idx++];
+      Modules[ID].FileName.assign(Record.begin() + Idx,
+                                  Record.begin() + Idx + NameLen);
+      Idx += NameLen;
+
+      // Dependencies
+      unsigned NumDeps = Record[Idx++];
+      Modules[ID].Dependencies.insert(Modules[ID].Dependencies.end(),
+                                      Record.begin() + Idx,
+                                      Record.begin() + Idx + NumDeps);
+      Idx += NumDeps;
+
+      // Make sure we're at the end of the record.
+      assert(Idx == Record.size() && "More module info?");
+
+      // Record this module as an unresolved module.
+      // FIXME: this doesn't work correctly for module names containing path
+      // separators.
+      StringRef ModuleName = llvm::sys::path::stem(Modules[ID].FileName);
+      // Remove the -<hash of ModuleMapPath>
+      ModuleName = ModuleName.rsplit('-').first;
+      UnresolvedModules[ModuleName] = ID;
+      break;
+    }
+
+    case IDENTIFIER_INDEX:
+      // Wire up the identifier index.
+      if (Record[0]) {
+        IdentifierIndex = IdentifierIndexTable::Create(
+            (const unsigned char *)Blob.data() + Record[0],
+            (const unsigned char *)Blob.data() + sizeof(uint32_t),
+            (const unsigned char *)Blob.data(), IdentifierIndexReaderTrait());
+      }
+      break;
+    }
+  }
+}
+
+GlobalModuleIndex::~GlobalModuleIndex() {
+  delete static_cast<IdentifierIndexTable *>(IdentifierIndex);
+}
+
+std::pair<GlobalModuleIndex *, llvm::Error>
+GlobalModuleIndex::readIndex(StringRef Path) {
+  // Load the index file, if it's there.
+  llvm::SmallString<128> IndexPath;
+  IndexPath += Path;
+  llvm::sys::path::append(IndexPath, IndexFileName);
+
+  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> BufferOrErr =
+      llvm::MemoryBuffer::getFile(IndexPath.c_str());
+  if (!BufferOrErr)
+    return std::make_pair(nullptr,
+                          llvm::errorCodeToError(BufferOrErr.getError()));
+  std::unique_ptr<llvm::MemoryBuffer> Buffer = std::move(BufferOrErr.get());
+
+  /// The main bitstream cursor for the main block.
+  llvm::BitstreamCursor Cursor(*Buffer);
+
+  // Sniff for the signature.
+  for (unsigned char C : {'B', 'C', 'G', 'I'}) {
+    if (Expected<llvm::SimpleBitstreamCursor::word_t> Res = Cursor.Read(8)) {
+      if (Res.get() != C)
+        return std::make_pair(
+            nullptr, llvm::createStringError(std::errc::illegal_byte_sequence,
+                                             "expected signature BCGI"));
+    } else
+      return std::make_pair(nullptr, Res.takeError());
+  }
+
+  return std::make_pair(new GlobalModuleIndex(std::move(Buffer), Cursor),
+                        llvm::Error::success());
+}
+
+void
+GlobalModuleIndex::getKnownModules(SmallVectorImpl<ModuleFile *> &ModuleFiles) {
+  ModuleFiles.clear();
+  for (unsigned I = 0, N = Modules.size(); I != N; ++I) {
+    if (ModuleFile *MF = Modules[I].File)
+      ModuleFiles.push_back(MF);
+  }
+}
+
+void GlobalModuleIndex::getModuleDependencies(
+       ModuleFile *File,
+       SmallVectorImpl<ModuleFile *> &Dependencies) {
+  // Look for information about this module file.
+  llvm::DenseMap<ModuleFile *, unsigned>::iterator Known
+    = ModulesByFile.find(File);
+  if (Known == ModulesByFile.end())
+    return;
+
+  // Record dependencies.
+  Dependencies.clear();
+  ArrayRef<unsigned> StoredDependencies = Modules[Known->second].Dependencies;
+  for (unsigned I = 0, N = StoredDependencies.size(); I != N; ++I) {
+    if (ModuleFile *MF = Modules[I].File)
+      Dependencies.push_back(MF);
+  }
+}
+
+bool GlobalModuleIndex::lookupIdentifier(StringRef Name, HitSet &Hits) {
+  Hits.clear();
+
+  // If there's no identifier index, there is nothing we can do.
+  if (!IdentifierIndex)
+    return false;
+
+  // Look into the identifier index.
+  ++NumIdentifierLookups;
+  IdentifierIndexTable &Table
+    = *static_cast<IdentifierIndexTable *>(IdentifierIndex);
+  IdentifierIndexTable::iterator Known = Table.find(Name);
+  if (Known == Table.end()) {
+    return true;
+  }
+
+  SmallVector<unsigned, 2> ModuleIDs = *Known;
+  for (unsigned I = 0, N = ModuleIDs.size(); I != N; ++I) {
+    if (ModuleFile *MF = Modules[ModuleIDs[I]].File)
+      Hits.insert(MF);
+  }
+
+  ++NumIdentifierLookupHits;
+  return true;
+}
+
+bool GlobalModuleIndex::loadedModuleFile(ModuleFile *File) {
+  // Look for the module in the global module index based on the module name.
+  StringRef Name = File->ModuleName;
+  llvm::StringMap<unsigned>::iterator Known = UnresolvedModules.find(Name);
+  if (Known == UnresolvedModules.end()) {
+    return true;
+  }
+
+  // Rectify this module with the global module index.
+  ModuleInfo &Info = Modules[Known->second];
+
+  //  If the size and modification time match what we expected, record this
+  // module file.
+  bool Failed = true;
+  if (File->File->getSize() == Info.Size &&
+      File->File->getModificationTime() == Info.ModTime) {
+    Info.File = File;
+    ModulesByFile[File] = Known->second;
+
+    Failed = false;
+  }
+
+  // One way or another, we have resolved this module file.
+  UnresolvedModules.erase(Known);
+  return Failed;
+}
+
+void GlobalModuleIndex::printStats() {
+  std::fprintf(stderr, "*** Global Module Index Statistics:\n");
+  if (NumIdentifierLookups) {
+    fprintf(stderr, "  %u / %u identifier lookups succeeded (%f%%)\n",
+            NumIdentifierLookupHits, NumIdentifierLookups,
+            (double)NumIdentifierLookupHits*100.0/NumIdentifierLookups);
+  }
+  std::fprintf(stderr, "\n");
+}
+
+LLVM_DUMP_METHOD void GlobalModuleIndex::dump() {
+  llvm::errs() << "*** Global Module Index Dump:\n";
+  llvm::errs() << "Module files:\n";
+  for (auto &MI : Modules) {
+    llvm::errs() << "** " << MI.FileName << "\n";
+    if (MI.File)
+      MI.File->dump();
+    else
+      llvm::errs() << "\n";
+  }
+  llvm::errs() << "\n";
+}
+
+//----------------------------------------------------------------------------//
+// Global module index writer.
+//----------------------------------------------------------------------------//
+
+namespace {
+  /// Provides information about a specific module file.
+  struct ModuleFileInfo {
+    /// The numberic ID for this module file.
+    unsigned ID;
+
+    /// The set of modules on which this module depends. Each entry is
+    /// a module ID.
+    SmallVector<unsigned, 4> Dependencies;
+    ASTFileSignature Signature;
+  };
+
+  struct ImportedModuleFileInfo {
+    off_t StoredSize;
+    time_t StoredModTime;
+    ASTFileSignature StoredSignature;
+    ImportedModuleFileInfo(off_t Size, time_t ModTime, ASTFileSignature Sig)
+        : StoredSize(Size), StoredModTime(ModTime), StoredSignature(Sig) {}
+  };
+
+  /// Builder that generates the global module index file.
+  class GlobalModuleIndexBuilder {
+    FileManager &FileMgr;
+    const PCHContainerReader &PCHContainerRdr;
+
+    /// Mapping from files to module file information.
+    typedef llvm::MapVector<const FileEntry *, ModuleFileInfo> ModuleFilesMap;
+
+    /// Information about each of the known module files.
+    ModuleFilesMap ModuleFiles;
+
+    /// Mapping from the imported module file to the imported
+    /// information.
+    typedef std::multimap<const FileEntry *, ImportedModuleFileInfo>
+        ImportedModuleFilesMap;
+
+    /// Information about each importing of a module file.
+    ImportedModuleFilesMap ImportedModuleFiles;
+
+    /// Mapping from identifiers to the list of module file IDs that
+    /// consider this identifier to be interesting.
+    typedef llvm::StringMap<SmallVector<unsigned, 2> > InterestingIdentifierMap;
+
+    /// A mapping from all interesting identifiers to the set of module
+    /// files in which those identifiers are considered interesting.
+    InterestingIdentifierMap InterestingIdentifiers;
+
+    /// Write the block-info block for the global module index file.
+    void emitBlockInfoBlock(llvm::BitstreamWriter &Stream);
+
+    /// Retrieve the module file information for the given file.
+    ModuleFileInfo &getModuleFileInfo(const FileEntry *File) {
+      llvm::MapVector<const FileEntry *, ModuleFileInfo>::iterator Known
+        = ModuleFiles.find(File);
+      if (Known != ModuleFiles.end())
+        return Known->second;
+
+      unsigned NewID = ModuleFiles.size();
+      ModuleFileInfo &Info = ModuleFiles[File];
+      Info.ID = NewID;
+      return Info;
+    }
+
+  public:
+    explicit GlobalModuleIndexBuilder(
+        FileManager &FileMgr, const PCHContainerReader &PCHContainerRdr)
+        : FileMgr(FileMgr), PCHContainerRdr(PCHContainerRdr) {}
+
+    /// Load the contents of the given module file into the builder.
+    llvm::Error loadModuleFile(const FileEntry *File);
+
+    /// Write the index to the given bitstream.
+    /// \returns true if an error occurred, false otherwise.
+    bool writeIndex(llvm::BitstreamWriter &Stream);
+  };
+}
+
+static void emitBlockID(unsigned ID, const char *Name,
+                        llvm::BitstreamWriter &Stream,
+                        SmallVectorImpl<uint64_t> &Record) {
+  Record.clear();
+  Record.push_back(ID);
+  Stream.EmitRecord(llvm::bitc::BLOCKINFO_CODE_SETBID, Record);
+
+  // Emit the block name if present.
+  if (!Name || Name[0] == 0) return;
+  Record.clear();
+  while (*Name)
+    Record.push_back(*Name++);
+  Stream.EmitRecord(llvm::bitc::BLOCKINFO_CODE_BLOCKNAME, Record);
+}
+
+static void emitRecordID(unsigned ID, const char *Name,
+                         llvm::BitstreamWriter &Stream,
+                         SmallVectorImpl<uint64_t> &Record) {
+  Record.clear();
+  Record.push_back(ID);
+  while (*Name)
+    Record.push_back(*Name++);
+  Stream.EmitRecord(llvm::bitc::BLOCKINFO_CODE_SETRECORDNAME, Record);
+}
+
+void
+GlobalModuleIndexBuilder::emitBlockInfoBlock(llvm::BitstreamWriter &Stream) {
+  SmallVector<uint64_t, 64> Record;
+  Stream.EnterBlockInfoBlock();
+
+#define BLOCK(X) emitBlockID(X ## _ID, #X, Stream, Record)
+#define RECORD(X) emitRecordID(X, #X, Stream, Record)
+  BLOCK(GLOBAL_INDEX_BLOCK);
+  RECORD(INDEX_METADATA);
+  RECORD(MODULE);
+  RECORD(IDENTIFIER_INDEX);
+#undef RECORD
+#undef BLOCK
+
+  Stream.ExitBlock();
+}
+
+namespace {
+  class InterestingASTIdentifierLookupTrait
+    : public serialization::reader::ASTIdentifierLookupTraitBase {
+
+  public:
+    /// The identifier and whether it is "interesting".
+    typedef std::pair<StringRef, bool> data_type;
+
+    data_type ReadData(const internal_key_type& k,
+                       const unsigned char* d,
+                       unsigned DataLen) {
+      // The first bit indicates whether this identifier is interesting.
+      // That's all we care about.
+      using namespace llvm::support;
+      unsigned RawID = endian::readNext<uint32_t, little, unaligned>(d);
+      bool IsInteresting = RawID & 0x01;
+      return std::make_pair(k, IsInteresting);
+    }
+  };
+}
+
+llvm::Error GlobalModuleIndexBuilder::loadModuleFile(const FileEntry *File) {
+  // Open the module file.
+
+  auto Buffer = FileMgr.getBufferForFile(File, /*isVolatile=*/true);
+  if (!Buffer)
+    return llvm::createStringError(Buffer.getError(),
+                                   "failed getting buffer for module file");
+
+  // Initialize the input stream
+  llvm::BitstreamCursor InStream(PCHContainerRdr.ExtractPCH(**Buffer));
+
+  // Sniff for the signature.
+  for (unsigned char C : {'C', 'P', 'C', 'H'})
+    if (Expected<llvm::SimpleBitstreamCursor::word_t> Res = InStream.Read(8)) {
+      if (Res.get() != C)
+        return llvm::createStringError(std::errc::illegal_byte_sequence,
+                                       "expected signature CPCH");
+    } else
+      return Res.takeError();
+
+  // Record this module file and assign it a unique ID (if it doesn't have
+  // one already).
+  unsigned ID = getModuleFileInfo(File).ID;
+
+  // Search for the blocks and records we care about.
+  enum { Other, ControlBlock, ASTBlock, DiagnosticOptionsBlock } State = Other;
+  bool Done = false;
+  while (!Done) {
+    Expected<llvm::BitstreamEntry> MaybeEntry = InStream.advance();
+    if (!MaybeEntry)
+      return MaybeEntry.takeError();
+    llvm::BitstreamEntry Entry = MaybeEntry.get();
+
+    switch (Entry.Kind) {
+    case llvm::BitstreamEntry::Error:
+      Done = true;
+      continue;
+
+    case llvm::BitstreamEntry::Record:
+      // In the 'other' state, just skip the record. We don't care.
+      if (State == Other) {
+        if (llvm::Expected<unsigned> Skipped = InStream.skipRecord(Entry.ID))
+          continue;
+        else
+          return Skipped.takeError();
+      }
+
+      // Handle potentially-interesting records below.
+      break;
+
+    case llvm::BitstreamEntry::SubBlock:
+      if (Entry.ID == CONTROL_BLOCK_ID) {
+        if (llvm::Error Err = InStream.EnterSubBlock(CONTROL_BLOCK_ID))
+          return Err;
+
+        // Found the control block.
+        State = ControlBlock;
+        continue;
+      }
+
+      if (Entry.ID == AST_BLOCK_ID) {
+        if (llvm::Error Err = InStream.EnterSubBlock(AST_BLOCK_ID))
+          return Err;
+
+        // Found the AST block.
+        State = ASTBlock;
+        continue;
+      }
+
+      if (Entry.ID == UNHASHED_CONTROL_BLOCK_ID) {
+        if (llvm::Error Err = InStream.EnterSubBlock(UNHASHED_CONTROL_BLOCK_ID))
+          return Err;
+
+        // Found the Diagnostic Options block.
+        State = DiagnosticOptionsBlock;
+        continue;
+      }
+
+      if (llvm::Error Err = InStream.SkipBlock())
+        return Err;
+
+      continue;
+
+    case llvm::BitstreamEntry::EndBlock:
+      State = Other;
+      continue;
+    }
+
+    // Read the given record.
+    SmallVector<uint64_t, 64> Record;
+    StringRef Blob;
+    Expected<unsigned> MaybeCode = InStream.readRecord(Entry.ID, Record, &Blob);
+    if (!MaybeCode)
+      return MaybeCode.takeError();
+    unsigned Code = MaybeCode.get();
+
+    // Handle module dependencies.
+    if (State == ControlBlock && Code == IMPORTS) {
+      // Load each of the imported PCH files.
+      unsigned Idx = 0, N = Record.size();
+      while (Idx < N) {
+        // Read information about the AST file.
+
+        // Skip the imported kind
+        ++Idx;
+
+        // Skip the import location
+        ++Idx;
+
+        // Load stored size/modification time.
+        off_t StoredSize = (off_t)Record[Idx++];
+        time_t StoredModTime = (time_t)Record[Idx++];
+
+        // Skip the stored signature.
+        // FIXME: we could read the signature out of the import and validate it.
+        ASTFileSignature StoredSignature = {
+            {{(uint32_t)Record[Idx++], (uint32_t)Record[Idx++],
+              (uint32_t)Record[Idx++], (uint32_t)Record[Idx++],
+              (uint32_t)Record[Idx++]}}};
+
+        // Skip the module name (currently this is only used for prebuilt
+        // modules while here we are only dealing with cached).
+        Idx += Record[Idx] + 1;
+
+        // Retrieve the imported file name.
+        unsigned Length = Record[Idx++];
+        SmallString<128> ImportedFile(Record.begin() + Idx,
+                                      Record.begin() + Idx + Length);
+        Idx += Length;
+
+        // Find the imported module file.
+        auto DependsOnFile
+          = FileMgr.getFile(ImportedFile, /*OpenFile=*/false,
+                            /*CacheFailure=*/false);
+
+        if (!DependsOnFile)
+          return llvm::createStringError(std::errc::bad_file_descriptor,
+                                         "imported file \"%s\" not found",
+                                         ImportedFile.c_str());
+
+        // Save the information in ImportedModuleFileInfo so we can verify after
+        // loading all pcms.
+        ImportedModuleFiles.insert(std::make_pair(
+            *DependsOnFile, ImportedModuleFileInfo(StoredSize, StoredModTime,
+                                                   StoredSignature)));
+
+        // Record the dependency.
+        unsigned DependsOnID = getModuleFileInfo(*DependsOnFile).ID;
+        getModuleFileInfo(File).Dependencies.push_back(DependsOnID);
+      }
+
+      continue;
+    }
+
+    // Handle the identifier table
+    if (State == ASTBlock && Code == IDENTIFIER_TABLE && Record[0] > 0) {
+      typedef llvm::OnDiskIterableChainedHashTable<
+          InterestingASTIdentifierLookupTrait> InterestingIdentifierTable;
+      std::unique_ptr<InterestingIdentifierTable> Table(
+          InterestingIdentifierTable::Create(
+              (const unsigned char *)Blob.data() + Record[0],
+              (const unsigned char *)Blob.data() + sizeof(uint32_t),
+              (const unsigned char *)Blob.data()));
+      for (InterestingIdentifierTable::data_iterator D = Table->data_begin(),
+                                                     DEnd = Table->data_end();
+           D != DEnd; ++D) {
+        std::pair<StringRef, bool> Ident = *D;
+        if (Ident.second)
+          InterestingIdentifiers[Ident.first].push_back(ID);
+        else
+          (void)InterestingIdentifiers[Ident.first];
+      }
+    }
+
+    // Get Signature.
+    if (State == DiagnosticOptionsBlock && Code == SIGNATURE)
+      getModuleFileInfo(File).Signature = {
+          {{(uint32_t)Record[0], (uint32_t)Record[1], (uint32_t)Record[2],
+            (uint32_t)Record[3], (uint32_t)Record[4]}}};
+
+    // We don't care about this record.
+  }
+
+  return llvm::Error::success();
+}
+
+namespace {
+
+/// Trait used to generate the identifier index as an on-disk hash
+/// table.
+class IdentifierIndexWriterTrait {
+public:
+  typedef StringRef key_type;
+  typedef StringRef key_type_ref;
+  typedef SmallVector<unsigned, 2> data_type;
+  typedef const SmallVector<unsigned, 2> &data_type_ref;
+  typedef unsigned hash_value_type;
+  typedef unsigned offset_type;
+
+  static hash_value_type ComputeHash(key_type_ref Key) {
+    return llvm::djbHash(Key);
+  }
+
+  std::pair<unsigned,unsigned>
+  EmitKeyDataLength(raw_ostream& Out, key_type_ref Key, data_type_ref Data) {
+    using namespace llvm::support;
+    endian::Writer LE(Out, little);
+    unsigned KeyLen = Key.size();
+    unsigned DataLen = Data.size() * 4;
+    LE.write<uint16_t>(KeyLen);
+    LE.write<uint16_t>(DataLen);
+    return std::make_pair(KeyLen, DataLen);
+  }
+
+  void EmitKey(raw_ostream& Out, key_type_ref Key, unsigned KeyLen) {
+    Out.write(Key.data(), KeyLen);
+  }
+
+  void EmitData(raw_ostream& Out, key_type_ref Key, data_type_ref Data,
+                unsigned DataLen) {
+    using namespace llvm::support;
+    for (unsigned I = 0, N = Data.size(); I != N; ++I)
+      endian::write<uint32_t>(Out, Data[I], little);
+  }
+};
+
+}
+
+bool GlobalModuleIndexBuilder::writeIndex(llvm::BitstreamWriter &Stream) {
+  for (auto MapEntry : ImportedModuleFiles) {
+    auto *File = MapEntry.first;
+    ImportedModuleFileInfo &Info = MapEntry.second;
+    if (getModuleFileInfo(File).Signature) {
+      if (getModuleFileInfo(File).Signature != Info.StoredSignature)
+        // Verify Signature.
+        return true;
+    } else if (Info.StoredSize != File->getSize() ||
+               Info.StoredModTime != File->getModificationTime())
+      // Verify Size and ModTime.
+      return true;
+  }
+
+  using namespace llvm;
+  llvm::TimeTraceScope TimeScope("Module WriteIndex");
+
+  // Emit the file header.
+  Stream.Emit((unsigned)'B', 8);
+  Stream.Emit((unsigned)'C', 8);
+  Stream.Emit((unsigned)'G', 8);
+  Stream.Emit((unsigned)'I', 8);
+
+  // Write the block-info block, which describes the records in this bitcode
+  // file.
+  emitBlockInfoBlock(Stream);
+
+  Stream.EnterSubblock(GLOBAL_INDEX_BLOCK_ID, 3);
+
+  // Write the metadata.
+  SmallVector<uint64_t, 2> Record;
+  Record.push_back(CurrentVersion);
+  Stream.EmitRecord(INDEX_METADATA, Record);
+
+  // Write the set of known module files.
+  for (ModuleFilesMap::iterator M = ModuleFiles.begin(),
+                                MEnd = ModuleFiles.end();
+       M != MEnd; ++M) {
+    Record.clear();
+    Record.push_back(M->second.ID);
+    Record.push_back(M->first->getSize());
+    Record.push_back(M->first->getModificationTime());
+
+    // File name
+    StringRef Name(M->first->getName());
+    Record.push_back(Name.size());
+    Record.append(Name.begin(), Name.end());
+
+    // Dependencies
+    Record.push_back(M->second.Dependencies.size());
+    Record.append(M->second.Dependencies.begin(), M->second.Dependencies.end());
+    Stream.EmitRecord(MODULE, Record);
+  }
+
+  // Write the identifier -> module file mapping.
+  {
+    llvm::OnDiskChainedHashTableGenerator<IdentifierIndexWriterTrait> Generator;
+    IdentifierIndexWriterTrait Trait;
+
+    // Populate the hash table.
+    for (InterestingIdentifierMap::iterator I = InterestingIdentifiers.begin(),
+                                            IEnd = InterestingIdentifiers.end();
+         I != IEnd; ++I) {
+      Generator.insert(I->first(), I->second, Trait);
+    }
+
+    // Create the on-disk hash table in a buffer.
+    SmallString<4096> IdentifierTable;
+    uint32_t BucketOffset;
+    {
+      using namespace llvm::support;
+      llvm::raw_svector_ostream Out(IdentifierTable);
+      // Make sure that no bucket is at offset 0
+      endian::write<uint32_t>(Out, 0, little);
+      BucketOffset = Generator.Emit(Out, Trait);
+    }
+
+    // Create a blob abbreviation
+    auto Abbrev = std::make_shared<BitCodeAbbrev>();
+    Abbrev->Add(BitCodeAbbrevOp(IDENTIFIER_INDEX));
+    Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+    Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
+    unsigned IDTableAbbrev = Stream.EmitAbbrev(std::move(Abbrev));
+
+    // Write the identifier table
+    uint64_t Record[] = {IDENTIFIER_INDEX, BucketOffset};
+    Stream.EmitRecordWithBlob(IDTableAbbrev, Record, IdentifierTable);
+  }
+
+  Stream.ExitBlock();
+  return false;
+}
+
+llvm::Error
+GlobalModuleIndex::writeIndex(FileManager &FileMgr,
+                              const PCHContainerReader &PCHContainerRdr,
+                              StringRef Path) {
+  llvm::SmallString<128> IndexPath;
+  IndexPath += Path;
+  llvm::sys::path::append(IndexPath, IndexFileName);
+
+  // Coordinate building the global index file with other processes that might
+  // try to do the same.
+  llvm::LockFileManager Locked(IndexPath);
+  switch (Locked) {
+  case llvm::LockFileManager::LFS_Error:
+    return llvm::createStringError(std::errc::io_error, "LFS error");
+
+  case llvm::LockFileManager::LFS_Owned:
+    // We're responsible for building the index ourselves. Do so below.
+    break;
+
+  case llvm::LockFileManager::LFS_Shared:
+    // Someone else is responsible for building the index. We don't care
+    // when they finish, so we're done.
+    return llvm::createStringError(std::errc::device_or_resource_busy,
+                                   "someone else is building the index");
+  }
+
+  // The module index builder.
+  GlobalModuleIndexBuilder Builder(FileMgr, PCHContainerRdr);
+
+  // Load each of the module files.
+  std::error_code EC;
+  for (llvm::sys::fs::directory_iterator D(Path, EC), DEnd;
+       D != DEnd && !EC;
+       D.increment(EC)) {
+    // If this isn't a module file, we don't care.
+    if (llvm::sys::path::extension(D->path()) != ".pcm") {
+      // ... unless it's a .pcm.lock file, which indicates that someone is
+      // in the process of rebuilding a module. They'll rebuild the index
+      // at the end of that translation unit, so we don't have to.
+      if (llvm::sys::path::extension(D->path()) == ".pcm.lock")
+        return llvm::createStringError(std::errc::device_or_resource_busy,
+                                       "someone else is building the index");
+
+      continue;
+    }
+
+    // If we can't find the module file, skip it.
+    auto ModuleFile = FileMgr.getFile(D->path());
+    if (!ModuleFile)
+      continue;
+
+    // Load this module file.
+    if (llvm::Error Err = Builder.loadModuleFile(*ModuleFile))
+      return Err;
+  }
+
+  // The output buffer, into which the global index will be written.
+  SmallVector<char, 16> OutputBuffer;
+  {
+    llvm::BitstreamWriter OutputStream(OutputBuffer);
+    if (Builder.writeIndex(OutputStream))
+      return llvm::createStringError(std::errc::io_error,
+                                     "failed writing index");
+  }
+
+  return llvm::writeFileAtomically(
+      (IndexPath + "-%%%%%%%%").str(), IndexPath,
+      llvm::StringRef(OutputBuffer.data(), OutputBuffer.size()));
+}
+
+namespace {
+  class GlobalIndexIdentifierIterator : public IdentifierIterator {
+    /// The current position within the identifier lookup table.
+    IdentifierIndexTable::key_iterator Current;
+
+    /// The end position within the identifier lookup table.
+    IdentifierIndexTable::key_iterator End;
+
+  public:
+    explicit GlobalIndexIdentifierIterator(IdentifierIndexTable &Idx) {
+      Current = Idx.key_begin();
+      End = Idx.key_end();
+    }
+
+    StringRef Next() override {
+      if (Current == End)
+        return StringRef();
+
+      StringRef Result = *Current;
+      ++Current;
+      return Result;
+    }
+  };
+}
+
+IdentifierIterator *GlobalModuleIndex::createIdentifierIterator() const {
+  IdentifierIndexTable &Table =
+    *static_cast<IdentifierIndexTable *>(IdentifierIndex);
+  return new GlobalIndexIdentifierIterator(Table);
+}